May 28, i 9 i7 Influence of Crop , Season , Water on Soil Bacteria 
325 
In every case the number of organisms is greater in the oat soil during 
the spring than in summer or fall, and with one exception they are greater 
in summer than in fall. While the difference is not as great nor as regular 
as might be desired, the tendency seems to be for the water to depress the 
number of organisms in oat soil. 
The ammonifying powers of the soil is higher in the summer than in 
the fall or spring, and there is a pronounced and regular difference between 
those receiving the various quantities of irrigation water in favor of those 
receiving the greatest quantity. While the difference is considerable 
throughout the season, it is more pronounced in the summer than at the 
time of taking the other samples. From an examination of the nitrifica¬ 
tion series one sees that this apparent increase in ammonia, due to water, 
may be caused in part by the depression of the nitrifying organisms, for 
the application of irrigation water to these soils has depressed the nitri¬ 
fying powers of the soil. This is quite pronounced at each season, and 
appears in the results for each specific year. Hence, it must be attributed 
to the water applied. 
CORN LAND 
The four com plots in this series received 37.5 inches, 25 inches, 15 
inches, and no irrigation water. Otherwise, they were all handled the 
same. The average summarized results for the three years are given in 
Table XXV. 
Table XXV .—Number of colonies of bacteria , milligrams of ammonia , and milligram 
of nitric nitrogen from soil receiving varying amounts of water. Crop, corn . Average 
for 3 years 
NUMBER OF COLONIES DEVELOPED IN 4 DAYS ON SYNTHETIC AGAR PER GRAM OF SOIL 
Plot No. 
Water 
applied. ! 
Sampled 
May 1. 
Sampled 
Aug. 1. 
Sampled 
Nov. a 8. 
Average. 
Inches. 
47 . 
37*5 
6 , 700, OOO 
6,866,000 
3 ) 333)000 
5,633, 000 
48 .. 
25.0 
4, 600, OOO 
5,800, OOO 
3,366,000 
4, 589) 000 
49 . 
15.0 
5 ? 933 j 000 
6,133,000 
2, 967,000 
5, 011,000 
50 ... 
None. 
6,100,000 
3, 867, 000 
4, 767,000 
4, 91 1, 000 
MILLIGRAMS OF 
AMMONIA PRODUCED IN IOO GM. OF SOIL IN 4 DAYS 
47 . 
37-5 
50.5 
59 *i 
46. 7 
52.1 
48. 
25.0 
55 * 2 
55 * * 
44*4 
51.8 
49 . 
IS.O 
50.5 
61.5 
43 * 2 
5 1 * 7 
5 ° . 
None. 
55 * 2 
57 * 2 
46.6 
53 *o 
MILLIGRAMS OF NITRIC NITROGEN PRODUCED IN IOO GM. OF SOIL IN 21 DAYS 
47 . 
37-5 
2.6 
7.6 
i*5 
3*9 
48. 
25.0 
1.9 
2.1 
o*5 
i *5 
49 . 
15.0 
2*3 
2. 2 
2.4 
2.3 
50 . 
None. 
1.9 
2.1 
i*5 
1. 8 
